The invention relates to sifting devices which utilize a screen to separate particles which are small enough to pass through the openings defined by the screen from particles which are too large to do so.
In recent years it has become of greater importance to recycle usable materials in almost all industries. For example, in the foundry industry finely ground sand is used to fashion a mold into which is poured molten metal. After the metal has cooled and solidified the excess sand is shaken off and the rough casting is then cut, ground, polished and otherwise treated until it is ready for the customer. The sand is returned to a storage bin for reuse. Throughout this process particles of the sand or "dirt" are mixed with particles of metal scrap. It is important to reuse as much of the sand and metal as possible, but first the two components must be separated.
In an iron foundry the task of separating the metal from the sand is simply accomplished by the use of a magnet; however, when working with non-ferrous metals such as aluminum or bronze the magnet technique is of course useless. Since the fine sand particles are for the most part smaller than the particles of metal it is possible to separate the two by sifting the mixture through a fine horizontal screen which may be made to vibrate; however, it has been found that this process is unsatisfactory in that the sand is usually moist and sticks together causing it to plug up or fall off the sides of the screen instead of sifting through the screen.
Where such problems as hereinabove stated exist, it has been found that an efficient and effective sifting process can be performed by the invention described hereinbelow.
The invention includes concentrically rotating inner and outer screened enclosures. The openings defined by the screen of the inner enclosure are larger than the openings defined by the screen of the outer enclosure. Material to be sifted is introduced into the inner enclosure through a chute at one axial end thereof. A dead plate or baffle member protects the screen from being damaged by the force of the incoming material. The axis of rotation is directed downwardly from the inlet end toward horizontal at an angle of 1 to 5 degrees, and preferably 2 degrees, so that the material entering through the inlet will slowly travel by the force of gravity toward the axial opposite end of the enclosures. The material which does not sift through both screened enclosures will eventually fall out the opposite end of the enclosures and the fine material which sifts through both screens during the rotation process may be used again.
The sifting device according to the present invention also includes a number of other novel features. There is provided a circular support surface radially outward of the inlet opening. The support surface rests on a pair of trunnion supported bearings for rotation of the support surface thereon. This structure allows for a large inlet opening which helps to prevent plugging of the inlet by the wet sand. At the opposite or outlet end of the device there is provided a support axle coincident with the axis of rotation, which axle is driven by a conventional motor and transmission system. The provision of this rotational mounting system allows for a central feed at the inlet end free of obstruction or the possibility of damaging critical moving parts, and for an outlet at the opposite end of the enclosures which is likewise free from the possibility of damage from the material being processed.
Also, there is provided lifting blades extending radially inwardly and substantially normal to the screens and parallel to the axis of rotation within each enclosure. These blades act to lift the material being processed and throw the material against the screens to help break up lumps of material.
Further, in order to prevent material from lodging in the screen and thus preventing efficient operation of the machine, there is provided a pressurized air supply line positioned outside the enclosures. The supply line runs parallel to the axis of rotation and includes a plurality of nozzles directed radially inward toward the screens. As the screen passes by the nozzles, a blast of air is directed toward the screen to disengage particles lodged in the screen. The nozzles each have a convex head with a linear slot therein running in the same direction as the supply line. Thus the blast of air eminating from the nozzles will be in the form of a thin wall of air directed along the entire length of the screen.
It is therefore one of the objects of the invention to provide a rotary sifting device which will effectively and efficiently separate fine particles from coarser particles by sifting material through a rotating screened enclosure.
Another object of the invention is to provide a support system for a rotary sifting machine which permits an inlet at one axial end thereof and an outlet at the opposite axial end thereof without obstruction or possibility of damage to the supporting moving parts.
Still another object of the invention is to provide a rotary sifting machine which introduces the material to be sifted to a first screen of relatively large openings and then to a second screen of relatively small openings.
It is a further object of the invention to provide means for disengaging material which may be lodged in the sifting screen during the sifting process.
It is a still further object of the invention to provide a means for pouring material into a rotary sifting device without damaging the screen area of the device.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.